Liquid crystal waveguides split optical fibre signal at MHz speed
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Optical power splitters (OPS) are used for optical power management in telecommunications networks, ensuring the important functions of splitting and combining optical signals in optical communications networks. By employing OPSs with variable power split ratio, the optical power can be redistributed in the network dynamically and in real-time, providing advantages such as improvement in network flexibility while maintaining the quality of transmission.
Optical fibres can also have sensors placed on them, the fibre serving in this case as transport medium for the sensor signal to the signal processing instrument for structural health monitoring, to measure changes in strain, temperature, pressure or displacement. Making use of reliable switches able to facilitate fast transmission of sensor signals to the processing unit, but to date, signals detected by the optical sensors placed on the fibres can be directed into the processing unit at a maximum rate of a few kHz. This means about 1000 measurements in a second and about 30 billion measurements in a year, but existing technologies such as opto-mechanical switches have limited switching speeds and lifetime due to their mechanical parts.
The OS/VOPS principle developed by IPMS makes use of an actively controllable guiding effect in electro-optical waveguides whereby light is guided inside an electro-optical layer along pathways defined by structured electrodes placed on both sides of this layer. Using highly transparent isotropic liquid crystal blends as a waveguide core layer element, Fraunhofer IPMS can control the optical power transmitted along the waveguide structure by adjusting the electro-optical Kerr response strength (the change in refractive index) in the liquid crystal layer, through an applied electrical field.
“With this device we could demonstrate sub-microsecond switching, and continuously voltage adjustable, full variable range power splitting at low optical loss” explained technology manager Dr. Florenta Costache in a statement.
The device can switch between channels at frequencies in the MHz range, which translates into up to one million measurements processed per second in the case of sensing fibres. As there are no moving parts (only the liquid crystals), the new switch could operate for much longer than current alternatives. In optical telecommunications networks, it could provide dynamic switching between different channels, controlling the power allocated to network nodes for better efficiency.
The device was developed for the telecommunication C-band centered around 1550 nm, but it can be optimized to operate at any other wavelength between 400 nm and 1600nm, says the German lab. It is fabricated at IPMS using precision silicon wafer level technology, using processes that would ramp up easily for cost efficient manufacturing.
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